Wireless technologies are evolving toward broadband information access across multiple networking platforms to meet demand for continuous availability of multimedia applications. Recent trends indicate that wide-area cellular networks based on second, third and fourth generation (“2G”, “3G” and “4G”) standards and wireless local area networks (“WLANs”) will co-exist to offer multimedia services to end users. Seamless mobility across the multiple networking platforms is needed to enhance interoperability and service continuity among the various wireless networks.
Mobility management provides universal wireless coverage and broadband access by strategically combining multiple networking platforms. During mobility management, the system may perform both intra-technology handoffs and inter-technology handoffs. Intra-technology handoffs include the traditional horizontal handoff process in which the mobile terminal hands-off between evolved Node-B (“eNB”), access points (“AP”) or base stations (“BS”) using the same access technology. Alternatively, inter-technology handoffs, commonly referred to as vertical handoffs (“VHO”), are performed when the mobile terminals roam between different access technologies.
VHO may include moving out of a preferred network (“MOUT”) or moving into a preferred network (“MIN”). For example, handoff procedures may be initiated when signal strength measurements originating in the primary network fall below pre-selected threshold parameters. The mobile terminal may detect the weak signal strength emanating from the primary network and may initiate a handoff to the secondary network having strong signal strength by reporting the weak signal to the primary network.
Frequently, during communication handoffs between access networks using different technologies, mobile terminals experience loss of service or service interruptions while negotiating the handoff exchange between the wireless access networks. One of the problems experienced during a handoff is that the mobile terminal does not know the appropriate open loop power needed to continue the call using the new network.
For any given access network, the direction of data flow is indicated by the terms “Forward Channel” (also known as “Forward Link) and “Reverse Channel” (“Reverse Link”). The Forward Channel contains communications travelling from the access network to the mobile terminal. The Reverse Channel includes communications travelling from the mobile terminal to the access network. The forward channel typically includes the Pilot Channel, MAC Channel, Control/Traffic Preamble, and Control/Traffic Channel. The Reverse Channel typically includes the Access Channel (“ACH”) and the Reverse Traffic Channel (“RTC”) depending upon the state of the data connection. The Access Channel is used by the mobile terminal to initiate communication with the access network. The mobile terminal uses the Reverse Traffic Channel to transmit user-specific data or signaling information to the access network.
Generally, when a mobile terminal originally places a call, it sends an access probe to the network on the access channel. The probe includes a call request. The mobile terminal gradually increases the power level until the call request is successfully completed. Then, the mobile terminal uses the power level established by the access probe to transmit the content of the call on the traffic channel. When the mobile terminal places subsequent calls, it retrieves the last successful power level from memory and uses this power level from the previous access probe as a starting point for the initial power estimation for a new access probe.
For example, for an Evolution-Data Optimized (“1×EV-DO”) network, also known as High Rate Packet Data (“HRPD”), the mobile terminal estimates the open loop power needed using the following method. When the mobile channel initiates a reverse traffic channel transmission (i.e., from the mobile terminal to the base station), the initial mean output power of the pilot channel of the RTC is set as the mean output power of the pilot channel at the end of the last access channel (“ACH”) probe minus the difference in the forward link (“FL”) mean received signal power from the end of the last ACH probe to the start of the RTC transmission. Thus, the initial mean power is based on the output power of the last successful access probe.
Use of the access probe is not desirable when the mobile terminal moves between networks during an active call because of the amount of time needed to establish a new connection. On the access channel, all mobile terminals requesting to place calls share a set bandwidth, thus the mobile terminal may experience a collision with other traffic when trying to connect with the new network, which may result in the first network dropping the call before the second network can successfully pick up the call. The amount of time needed to iterate an appropriate power level may also result in the call being dropped.
Instead, the call is transferred directly from one network to another network, for example, from a 3rd Generation (“3G”) Long Term Evolution (“LTE”) network to a HRPD network, using only the traffic channel in order to reduce the call interruption time. However, there is currently no defined method for the mobile terminal to determine what initial open loop power level should be used on the reverse traffic channel.
Therefore, what is needed is a method and system for a mobile terminal to determine an initial open loop power for a pilot channel of the reverse traffic channel when handing-off an active phone call between networks that use different access technologies.